We all live in a world where one cannot do without material things. Things like food, clothing, a house among many others are essential for life. A person would not be able to survive in their absence.
As none of these are available for free, one has to earn money. And to earn money one has to work. This makes it clear that money is one of the motives why people work. Though earning money should not be mistaken as the only motive for people working. Work in many cases gives people joy, a sense of achievement, satisfaction and many things that cannot be replaced by money. People continue with a particular profession because they enjoy their work, and do not want to shift to a higher paying job even if they could earn more as money is not the only objective why they're doing what they are.